SUSE: 2019:0891-1 Important: Xen Denial of Service Fixes

This update for xen fixes the following issues: Security issues fixed: - Fixed an issue which could allow malicious PV guests may cause a host crash or gain access to data pertaining to other guests.Additionally, vulnerable configurations are likely to be unstable even in the absence of an attack (bsc#1126198). - Fixed multiple access violations introduced by XENMEM_exchange hypercall which could allow a single PV guest to leak arbitrary amounts of memory, leading to a denial of service (bsc#1126192). - Fixed an issue which could allow a malicious unprivileged guest userspace process to escalate its privilege to that of other userspace processes in the same guest and potentially thereby to that of the guest operating system (bsc#1126201). - Fixed an issue which could allow malicious or buggy x86 PV guest kernels